| Summary: | 碩士 === 國立臺灣大學 === 食品科技研究所 === 93 === Recently, many chronic diseases such as cancer, atherosclerosis, and aging were found to be associated with oxidative damage. The imbalance between the concentration of reactive oxygen and nitrogen species and defense mechanisms of the body would cause oxidative damage, and antioxidants enhancement would reduce oxidative damage. Therefore, dietary supplementation of antioxidants was thought to be beneficial to health. The purpose of this study is to locate the most antioxidative solvent extract of Longan (Dimorcarpus longan Lour.) flower by various antioxidative assays, and to further investigate the most efficient antioxidative fraction after chromatographic separation by the assay of Cu2+-induced low density lipoprotein (LDL) oxidation.
First, the crude extracts were prepared by extracting Longan flower with boiling water and four solvents (95% ethanol, methanol, ethyl acetate and n-hexane) at room temperature. Then the five different solvent extracts of Longan flower were tested for various antioxidative assays, including DPPH free radical scavenging effect, Trolox equivalent antioxidant capacity (TEAC) assay, oxygen radical absorbance capacity (ORAC) assay, reducing power, inhibition of peroxidation in a liposome model system, Cu2+-induced oxidation of human LDL and recovery effect of TGF-β1 induced oxidative damage in Hep 3B cells.
The results of antioxidative assays revealed that the best effect was exhibited by the water extract, followed by methanol, ethanol, ethyl acetate and n-hexane extracts of Longan flower. The EC50 value of water extract in scavenging DPPH radicals was 3.69±0.16 μg/mL. Results of TEAC and ORAC assays revealed that water extract gave the highest TEAC value (1.22 mM Trolox equivalent) and ORAC value (7.28 mM Trolox equivalent). With regard to reducing power, at sample concentration of 50 μg/mL, water extract gave the best effect. Concerning inhibition of peroxidation in a liposome model system, the IC50 of water extract in inhibiting the peroxidation was 54.46±1.61 μg/mL, which was the lowest among all the extracts. As for the effect of Cu2+-induced oxidation of human LDL, water extract showed the best effect in delaying LDL oxidation. Finally, water extract gave the best recovery effect of TGF-β1 induced oxidative damage in Hep 3B cells at concentration of 100 μg/mL.
Water extract of Longan flower contained the most abundant amount of total polyphenol (548.2±12.7 mg gallic acid equivalent / g of dry weight) and gallic acid (10.4 ± 0.3 mg gallic acid /g of dry weight). According to the results of antioxidative assays, water extract showed the highest antioxidant capacity and we presumed that this could probably be related to the phenolic compounds. Then Sephadex LH-20 gel chromatography was employed to fractionate the water extract; eight fractions were obtained and tested for Cu2+-induced oxidation of human LDL. The result of antioxidative experiment revealed that fraction 7 showed the best effect in delaying LDL oxidation. We presumed that antioxidative capacity of Longan flower could probably be related to phenol compounds having higher polarity.
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